I'm trying to create a Facebook application that displays a friend invite dialog within the application using Facebook's Javascript API (FB.ui).

To do that I followed this tutorial

I have two problems :

1. The action url I've put in the request-form is "http://apps.facebook.com/appname/post_invite.php" but I see that the iframe source after the post is "http://mydomain.com/post_invite.php" and when this iframe tries to do : parent.closeInviteWidget(); I get an error saying :

   "Permission denied for < http: //mydomain.com > (document.domain has not been set) to get property Window.closeInviteWidget from < http:// apps.facebook.com> (document.domain=< http:// facebook.com>)."

2. The skip button inside the request-form opens the action url in a new window (new browser tab) and not post to itself like the invite button.

How can I fix those problems?

-------------------- UPDATE : --------------------------------

I've tried to do what ifaour said and changed the code to :

function inviteFriends(user_name, category_id, category_name)
{
    url = appBaseUrl + "/index.php?category_id=" + category_id;
    req = "<fb:req-choice url='" + url + "' label='Authorize My Application' />";
    content = user_name + " opened a new category called " + category_name + ". " + req;
    action = 'post_invite.php';

    fbmi_text = '<fb:request-form action="' + action + '" target="_self" method="post" invite="true" type="Invite" content="' + content + '" <fb:multi-friend-selector showborder="false" actiontext="Invite yor friends" email_invite="false" import_external_friends="false" /> </fb:request-form>';

    FB.ui({
    method:'fbml.dialog',
    width:'750px',
    fbml:fbmi_text
     });
}

When I use FireBug and look at the invite form it looks like this:

<form id="req_form_4d20682f73ddb6e71722794" content="I've opened a new category called dsfsd. <fb:req-choice url='http://apps.facebook.com/appname/index.php?category_id=60' label='Authorize My Application' /> type="Invite" invite="true" method="post" target="_self" action="http://apps.facebook.com/appname/post_invite.php">
...
</form>

But I still get the same error :

Permission denied for <http://mydomain.com> (document.domain has not been set) to get property Window.closeInviteWidget from <http://apps.facebook.com> (document.domain=<http://facebook.com>)...